U.S. patent application number 16/678651 was filed with the patent office on 2020-05-14 for cooling system for power transmission unit.
The applicant listed for this patent is Toyota Jidosha Kabushiki Kaisha. Invention is credited to Kensei Hata, Shotaro Kato, Akiko Nishimine, So Okita, Masashi Shinoda.
Application Number | 20200149624 16/678651 |
Document ID | / |
Family ID | 70469084 |
Filed Date | 2020-05-14 |
United States Patent
Application |
20200149624 |
Kind Code |
A1 |
Hata; Kensei ; et
al. |
May 14, 2020 |
COOLING SYSTEM FOR POWER TRANSMISSION UNIT
Abstract
A cooling system for a power transmission unit that can supply
oil properly to a differential mechanism and motors. The cooling
system comprises: a first branch passage to supply the oil to the
differential mechanism; a second branch passage to supply the oil
to the first motor; and a third branch passage to supply the oil to
the second motor. The second branch passage includes a first oil
feeding section that supplies the oil to a coil of the first motor,
and a second oil feeding section that supplies the oil f to a core
of the first motor. The third branch passage includes a third oil
feeding section that supplies the oil to a coil of the second
motor, and a fourth oil feeding section that supplies the oil to a
core of the second motor.
Inventors: |
Hata; Kensei; (Shizuoka-ken,
JP) ; Nishimine; Akiko; (Susono-shi, JP) ;
Kato; Shotaro; (Shizuoka-ken, JP) ; Shinoda;
Masashi; (Shizuoka-ken, JP) ; Okita; So;
(Anjo-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Toyota Jidosha Kabushiki Kaisha |
Toyota-shi |
|
JP |
|
|
Family ID: |
70469084 |
Appl. No.: |
16/678651 |
Filed: |
November 8, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02K 9/19 20130101; F16H
41/30 20130101; H02K 7/116 20130101; B60K 6/48 20130101; F16H
57/0435 20130101; F16H 57/0476 20130101; F16H 57/0456 20130101;
H02K 7/006 20130101; F16H 57/0423 20130101; F16H 57/0441 20130101;
H02K 1/32 20130101; F01P 11/08 20130101 |
International
Class: |
F16H 57/04 20060101
F16H057/04; F16H 41/30 20060101 F16H041/30; H02K 7/116 20060101
H02K007/116; F01P 11/08 20060101 F01P011/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 12, 2018 |
JP |
2018-212336 |
Claims
1. A cooling system for a power transmission unit, comprising: an
engine; a first motor having a generating function; a differential
mechanism that distributes a torque of the engine to the first
motor and drive wheels; and a second motor that is driven by an
electric power generated by the first motor to generate a torque to
be synthesized with a torque transmitted from the differential
mechanism to the drive wheels, the cooling system comprising: an
oil pump that pumps up an oil from an oil pan, and that supplies
the oil to the first motor, the second motor, and the differential
mechanism; an oil cooler that cools the oil; a cyclic oil passage
that connects the oil pump and the oil cooler to circulate the oil
between the oil pump and the oil cooler, a first branch passage
that is branched from the cyclic oil passage to supply the oil to
the differential mechanism; a second branch passage that is
branched from the cyclic oil passage at downstream of the first
branch passage to supply the oil to the first motor; and a third
branch passage that is branched from the cyclic oil passage in
parallel to the second branch passage, at downstream of the first
branch passage to supply the oil to the second motor, wherein the
second branch passage includes a first oil feeding section that
supplies the oil flowing through the second branch passage to a
coil of the first motor at least partially, and a second oil
feeding section that supplies the remaining oil flowing through the
second branch passage to a core of the first motor, and the third
branch passage includes a third oil feeding section that supplies
the oil flowing through the third branch passage to a coil of the
second motor at least partially, and a fourth oil feeding section
that supplies the remaining oil flowing through the third branch
passage to a core of the second motor.
2. The cooling system for the power transmission unit as claimed in
claim 1, wherein the second oil feeding section is formed
downstream of the first oil feeding section, and the fourth oil
feeding section is formed downstream of the third oil feeding
section.
3. The cooling system for the power transmission unit as claimed in
claim 1, wherein the power transmission unit further comprises a
case that holds the first motor and the second motor, the first oil
feeding section is situated above the first motor in the case, the
third oil feeding section is situated above the second motor in the
case, the second branch passage further includes a first
intermediate section extending outside of the case between the
first oil feeding section and the second oil feeding section, and
the third branch passage further includes a second intermediate
section extending outside of the case between the third oil feeding
section and the fourth oil feeding section.
4. The cooling system for the power transmission unit as claimed in
claim 2, wherein the power transmission unit further comprises a
case that holds the first motor and the second motor, the first oil
feeding section is situated above the first motor in the case, the
third oil feeding section is situated above the second motor in the
case, the second branch passage further includes a first
intermediate section extending outside of the case between the
first oil feeding section and the second oil feeding section, and
the third branch passage further includes a second intermediate
section extending outside of the case between the third oil feeding
section and the fourth oil feeding section.
5. The cooling system for the power transmission unit as claimed in
claim 1, wherein the first branch passage is branched from the
cyclic oil passage upstream of the oil cooler, and the second
branch passage and the third branch passage are branched from the
cyclic oil passage downstream of the oil cooler.
6. The cooling system for the power transmission unit as claimed in
claim 2, wherein the first branch passage is branched from the
cyclic oil passage upstream of the oil cooler, and the second
branch passage and the third branch passage are branched from the
cyclic oil passage downstream of the oil cooler.
7. The cooling system for the power transmission unit as claimed in
claim 3, wherein the first branch passage is branched from the
cyclic oil passage upstream of the oil cooler, and the second
branch passage and the third branch passage are branched from the
cyclic oil passage downstream of the oil cooler.
8. The cooling system for the power transmission unit as claimed in
claim 4, wherein the first branch passage is branched from the
cyclic oil passage upstream of the oil cooler, and the second
branch passage and the third branch passage are branched from the
cyclic oil passage downstream of the oil cooler.
9. The cooling system for the power transmission unit as claimed in
claim 1, further comprising: an orifice that is arranged on the
first branch passage.
10. The cooling system for the power transmission unit as claimed
in claim 2, further comprising: an orifice that is arranged on the
first branch passage.
11. The cooling system for the power transmission unit as claimed
in claim 3, further comprising: an orifice that is arranged on the
first branch passage.
12. The cooling system for the power transmission unit as claimed
in claim 4, further comprising: an orifice that is arranged on the
first branch passage.
13. The cooling system for the power transmission unit as claimed
in claim 5, further comprising: an orifice that is arranged on the
first branch passage.
14. The cooling system for the power transmission unit as claimed
in claim 6, further comprising: an orifice that is arranged on the
first branch passage.
15. The cooling system for the power transmission unit as claimed
in claim 7, further comprising: an orifice that is arranged on the
first branch passage.
16. The cooling system for the power transmission unit as claimed
in claim 8, further comprising: an orifice that is arranged on the
first branch passage.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of priority to
Japanese Patent Application No. 2018-212336 filed on Nov. 12, 2018
with the Japanese Patent Office.
BACKGROUND
Field of the Disclosure
[0002] Embodiments of the present disclosure relate to the art of a
cooling system for a power transmission unit that transmits an
engine torque to drive wheels, and more especially, to a cooling
system that cools a power transmission unit including an engine and
a motor-generator by oil.
Discussion of the Related Art
[0003] US 2010/0120569 A describes one example of the cooling
system for the power transmission device of this kind. In a driving
apparatus taught by US 2010/0120569 A1, a prime mover includes an
engine, a first motor-generator, and a second motor-generator, and
a differential gear mechanism is arranged in the driving apparatus
to distribute a power of the engine to the first motor-generator
and to an output gear. A torque of the second motor-generator is
synthesized with a torque delivered from an output gear to drive
wheels. According to the teachings US 2010/0120569 A1, an oil pump
is driven by the torque of the engine, and the differential gear
mechanism is cooled and lubricated by an oil supplied from the oil
pump through an oil passage formed in an input shaft of the
differential gear mechanism.
[0004] As a result of energizing the conventional motor-generator,
the motor-generator may be heated by Joule heat and fractional heat
resulting from a rotation of a rotor. Therefore, it is necessary to
cool the motor-generator by oil. However, an amount of heat
generation in the motor-generator is different from an amount of
heat generation in the differential gear mechanism. That is, a
required amount of the oil for cooling the motor-generator is
different from a required amount of the oil for cooling the
differential gear mechanism. In order to cool both of the
motor-generator and the differential gear mechanism properly by
supplying ample amount of the oil to the motor-generator and the
differential gear mechanism, the conventional cooling systems have
to be improved.
SUMMARY
[0005] Aspects of the present disclosure have been conceived noting
the foregoing technical problems, and it is therefore an object of
the present disclosure to provide a cooling system for a power
transmission unit that can supply oil properly to a differential
mechanism and a motor.
[0006] The cooling system according to the embodiment of the
present disclosure is applied to a power transmission unit,
comprising: an engine; a first motor having a generating function;
a differential mechanism that distributes a torque of the engine to
the first motor and drive wheels; and a second motor that is driven
by an electric power generated by the first motor to generate a
torque to be synthesized with a torque transmitted from the
differential mechanism to the drive wheels. The cooling system
comprise: an oil pump that pumps up an oil from an oil pan, and
that supplies the oil to the first motor, the second motor, and the
differential mechanism; an oil cooler that cools the oil; and a
cyclic oil passage that connects the oil pump and the oil cooler to
circulate the oil between the oil pump and the oil cooler. In order
to achieve the above-explained objective, according to the
embodiment of the present disclosure, the cooling system comprise
is provided with: a first branch passage that is branched from the
cyclic oil passage to supply the oil to the differential mechanism;
a second branch passage that is branched from the cyclic oil
passage at downstream of the first branch passage to supply the oil
to the first motor; and a third branch passage that is branched
from the cyclic oil passage in parallel to the second branch
passage, at downstream of the first branch passage to supply the
oil to the second motor. The second branch passage includes a first
oil feeding section that supplies the oil flowing through the
second branch passage to a coil of the first motor at least
partially, and a second oil feeding section that supplies the
remaining oil flowing through the second branch passage to a core
of the first motor. The third branch passage includes a third oil
feeding section that supplies the oil flowing through the third
branch passage to a coil of the second motor at least partially,
and a fourth oil feeding section that supplies the remaining oil
flowing through the third branch passage to a core of the second
motor.
[0007] In a non-limiting embodiment, the second oil feeding section
may be formed downstream of the first oil feeding section, and the
fourth oil feeding section may be formed downstream of the third
oil feeding section.
[0008] In a non-limiting embodiment, the power transmission unit
may further comprise a case that holds the first motor and the
second motor. The first oil feeding section may be situated above
the first motor in the case, and the third oil feeding section may
be situated above the second motor in the case. The second branch
passage may further include a first intermediate section extending
outside of the case between the first oil feeding section and the
second oil feeding section, and the third branch passage may
further include a second intermediate section extending outside of
the case between the third oil feeding section and the fourth oil
feeding section.
[0009] In a non-limiting embodiment, the first branch passage may
be branched from the cyclic oil passage upstream of the oil cooler,
and the second branch passage and the third branch passage may be
branched from the cyclic oil passage downstream of the oil
cooler.
[0010] In a non-limiting embodiment, the cooling system may further
comprise an orifice that is arranged on the first branch
passage.
[0011] Thus, according to the exemplary embodiment of the present
disclosure, the oil discharged from the oil pump circulate within
the cyclic oil passage is partially delivered to the differential
mechanism through the first branch passage branched from the cyclic
oil passage. The remaining oil in the cyclic oil passage is
delivered to the first motor through the second branch passage and
to the third motor through the third branch passage branched from
the cyclic oil passage downstream of the first branch passage
respectively. However, an orifice or the like is not arranged on
the cyclic oil passage. For this reason, an energy loss of the oil
pump derived from an increase in a pressure loss in the cyclic oil
passage can be reduced with a simple structure. In addition, since
each of the branch passages are branched from the cyclic oil
passage toward the differential mechanism, the first motor, and the
second motor respectively, the oil may be delivered to the
differential mechanism, the first motor, and the second motor in
appropriate amounts. Moreover, since the oil cooled by the oil
cooler is delivered to the first motor and the second motor, the
first motor and the second motor may be cooled efficiently.
Further, since the second branch passage and the third branch
passage are formed in parallel, a pressure loss in the cyclic oil
passage will not be increased compared to a case in which the
second branch passage and the third branch passage are formed in
series. Furthermore, the second branch passage comprises the first
oil feeding section for feeding the oil to the coil of the first
motor, and the second oil feeding section for feeding the oil to
the core of the first motor. Likewise, the third branch passage
comprises the third oil feeding section for feeding the oil to the
coil of the second motor, and the fourth oil feeding section for
feeding the oil to the core of the second motor. For this reason,
amounts of the oil to be supplied to the coil and the core of each
motor may be differentiated to cool the motor efficiently.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Features, aspects, and advantages of exemplary embodiments
of the present disclosure will become better understood with
reference to the following description and accompanying drawings,
which should not limit the disclosure in any way.
[0013] FIG. 1 is a schematic illustration showing one example of
the power transmission unit of a vehicle to which the cooling
system according to the exemplary embodiment of the present
disclosure is applied;
[0014] FIG. 2 is a circuit diagram showing one example of a
structure of oil passages for supplying oil to a power split
mechanism etc.;
[0015] FIG. 3 is a partial cross-sectional view showing a part of a
cross-section of the power transmission unit;
[0016] FIG. 4 is a partial cross-sectional view showing a part of a
cross-section of the oil passage for supplying the oil to the first
motor in an enlarged scale; and
[0017] FIG. 5 is a partial cross-sectional view showing a part of a
cross-section of the oil passage for supplying the oil to the
second motor in an enlarged scale.
DETAILED DESCRIPTION
[0018] Referring now to FIG. 1, there is shown one example of a
power transmission unit of a hybrid vehicle (as will be simply
called the "vehicle" hereinafter) to which the cooling system
according to the exemplary embodiment of the present disclosure is
applied. A prime mover of the vehicle comprises an engine (referred
to as ENG in FIG. 1) 1, a first motor (referred to as MG1 in FIG.
1) 2, and a second motor (referred to as MG2 in FIG. 1) 3. In the
vehicle, an output power of the engine 1 is distributed to the
first motor 2 and drive wheels 5 through a power split mechanism 4
as a differential mechanism. An electric power generated by the
first motor 2 may be supplied to the second motor 3 to operate the
second motor 3 as a motor, and torque generated by the second motor
3 may be delivered to the drive wheels 5.
[0019] Each of the first motor 2 and the second motor 3 is a
motor-generator that is operated not only as a motor to generate
torque by applying electricity thereto, but also as a generator to
generate electricity by applying torque thereto. For example, a
permanent magnet synchronous motor and an AC motor such as an
induction motor may be used as the first motor 2 and the second
motor 3, respectively.
[0020] In the example shown in FIG. 1, a single-pinion planetary
gear unit is employed as the power split mechanism 4. Specifically,
the power split mechanism 4 comprises a sun gear 4s, a ring gear 4r
as an internal gear that is arranged concentrically with the sun
gear 4s, a plurality of planetary gears 4p interposed between the
sun gear 4s and the ring gear 4r, and a carrier 4c supporting the
planetary gears 4p in a rotatable manner.
[0021] The first motor 2 is disposed between the oil pump 6 and the
power split mechanism 4, and the carrier 4c of the power split
mechanism 4 is mounted on an output shaft 1a of the engine 1. In
the first motor 2, a hollow rotary shaft 2a that is rotated
integrally with a rotor 2b is connected to a hollow rotary shaft of
the sun gear 4s of the power split mechanism 4. A rotary shaft 6a
of the oil pump 6 penetrates through the rotary shaft 2a and the
sun gear 4s to be connected to an input shaft 4a of the power split
mechanism 4.
[0022] A first drive gear 7 as an external gear is integrally
formed around the ring gear 4r of the power split mechanism 4, and
a countershaft 8 is arranged in parallel with a common rotational
axis of the power split mechanism 4 and the first motor 2. A
counter driven gear 9 is fitted onto one end of the countershaft 8
(i.e., right side in FIG. 1) to be rotated integrally therewith
while being meshed with the first drive gear 7, and a counter drive
gear 10 is fitted onto the other end of the countershaft 8 (i.e.,
left side in FIG. 1) to be rotated integrally therewith while being
meshed with a differential ring gear 12 of a differential gear unit
11 as a final reduction. Thus, the ring gear 4r of the power split
mechanism 4 is connected to the drive wheel 5 through an output
gear train 13 including the first drive gear 7, the countershaft 8,
the counter driven gear 9, the counter drive gear 10, and the
differential ring gear 12.
[0023] In the power transmission unit of the vehicle, an output
torque of the second motor 3 can be added to the torque delivered
from the power split mechanism 4 to the drive wheels 5. To this
end, a rotary shaft 3a of the second motor 3 extends in parallel
with the countershaft 8, and a second drive gear 14 is fitted onto
a leading end of the rotary shaft 3a to be rotated integrally
therewith while being meshed with the counter driven gear 9. The
second drive gear 14 is diametrically larger than the counter
driven gear 9 so that the output torque of the second motor 3 is
multiplied by the second drive gear 14. That is, the output gear
train 13 serves as a speed reducing section in which the counter
driven gear 9 and the second drive gear 14 serve as a speed
reducing mechanism.
[0024] Next, an oil feeding system for supplying oil to the power
split mechanism 4 and the motors 2 and 3 will be explained with
reference to FIG. 2. As illustrated in FIG. 2, the power
transmission unit is held in a transmission case 15. The
transmission case 15 includes a motor case 16, an end cover 17, and
a gear case 18. Specifically, the motor case 16 is a cylindrical
case, and the first motor 2 and the second motor 3 are held in the
motor case 16. One of openings of the motor case 16 is closed by
the end cover 17.
[0025] The gear case 18 also as a cylindrical case is arranged in
an opposite side to the end cover 17 across the motor case 16, and
the power split mechanism 4, the differential gear unit 11, the
output gear train 13 etc. are held in the gear case 18. The motor
case 16 and the gear case 18 are joined to each other through a
center support 19. The rotary shaft 2a of the first motor 2 and the
rotary shaft 3a of the second motor 3 penetrate through the center
support 19 while being supported in a rotatable manner by bearings
(not shown) respectively. In the transmission case 15, accordingly,
an internal space enclosed by the motor case 16, the end cover 17,
and the center support 19 serves as a motor chamber, and an
internal space enclosed by the gear case 18 and the center support
19 serves as a gear chamber.
[0026] In order to cool and lubricate the first motor 2, the second
motor 3, the power split mechanism 4 and so on, the oil is
circulated in the transmission case 15. An oil pan (not shown) is
formed on a bottom of the transmission case 15, and the
differential ring gear 12 is immersed at least partially in the oil
held in the oil pan. When the differential ring gear 12 is rotated
by torque, the oil held in the oil pan is splashed by the
differential ring gear 12 to be applied to the differential gear
unit 11, the output gear train 13 and so on.
[0027] The oil applied to the differential gear unit 11, the output
gear train 13 and so on drips to the oil pan, and pumped up by the
oil pump 6 to an oil cooler 21 through a strainer 20. The oil
cooled by the oil cooler 21 is returned to the oil pan again. To
this end, a cyclic oil passage 22 is formed between the oil pan and
the oil cooler 21. Specifically, an outlet (not shown) of the oil
pump 6 is connected to the oil cooler 21 through a first oil
passage 23, and the oil cooled by the oil cooler 21 is returned to
the oil pan through a second oil passage 24. As illustrated in FIG.
2, the first oil passage 23 and the second oil passage 24 are
formed in the center support 19. For example, a conventional
water-cooling system may be adopted as the oil cooler 21, and the
oil cooler 21 cools the oil by exchanging heat between the oil and
water. Heat of the water that is warmed as a result of such heat
exchange between the oil and the water is radiated to the external
atmosphere through a radiator (not shown).
[0028] The first oil passage 23 is branched into a first branch
passage 25 upstream of the oil cooler 21 at a branching point 25a.
Specifically, the first branch passage 25 is formed mainly of a
pipe, and oriented to the power split mechanism 4. In order to
reduce a flow rate of the oil flowing through the first branch
passage 25, an orifice 26 is arranged on the first branch passage
25. That is, a flow rate of the oil flowing through the first oil
passage 23 is larger than a flow rate of the oil flowing through
the first branch passage 25.
[0029] A plurality of relief valves 27 are arranged downstream of
the branching point 25a of the first branch passage 25 on the first
oil passage 23. According to the example shown in FIG. 2,
specifically, two relief valves 27 are arranged in parallel on the
first oil passage 23. Each of the relief valves 27 is opened when a
hydraulic pressure in the cyclic oil passage 22 is raised to a
predetermined level thereby discharging the oil from the cyclic oil
passage 22 to the oil pan. Consequently, an internal pressure of
the cyclic oil passage 22 is reduced lower than the predetermined
level.
[0030] The second oil passage 24 is branched into a second branch
passage 28 to supply the oil to the first motor 2, and a third
branch passage 29 to supply the oil to the second motor 3. The
second branch passage 28 and the third branch passage 29 are also
formed mainly of a pipe, respectively, and branched from the second
oil passage 24 in parallel to each other. Specifically, the second
branch passage 28 is branched from the second oil passage 24 at a
branching point 28a that is downstream of the branching point 25a
of the first branch passage 25. The second branch passage 28
comprises: a first upper outlet section 30 as a first oil feeding
section that supplies the oil to a coil 2c of the first motor 2
from above; a first core cooling section 31 as a second oil feeding
section that supplies the oil to a core of the first motor 2 from
inside; and a first intermediate section 32 extending between the
first upper outlet section 30 and the first core cooling section
31.
[0031] The first upper outlet section 30 extends substantially
parallel to a center axis C.sub.MG1 of the first motor 2. In order
to supply the oil to the coil 2c of the first motor 2 from above,
as shown in FIG. 3, the first upper outlet section 30 is situated
above the first motor 2 in the motor case 16. FIG. 4 shows a
structure of the first upper outlet section 30 in more detail in an
enlarged scale. As illustrated in FIG. 4, a plurality of outlet
holes 30a are formed in the first upper outlet section 30 in such a
manner as to penetrate through the pipe forming the first upper
outlet section 30 in a thickness direction. As indicated by the
arrows in FIG. 3, the oil flowing through the first upper outlet
section 30 drips from the outlet holes 30a to the coil 2c of the
first motor 2 thereby drawing the heat of the coil 2c of the first
motor 2. Then, the oil further drips from the coil 2c of the first
motor 2 to the oil pan, and pumped up again by the oil pump 6 to
the oil cooler 21 to be cooled again. In FIG. 3, only the center
axis C.sub.MG1 of the first motor 2, a center axis C.sub.MG2 of the
second motor 3, a center axis C.sub.C of the countershaft 8, and a
center axis C.sub.DTF of the differential gear unit 11 are
indicated for the sake of illustration.
[0032] As illustrated in FIGS. 2 and 4, the first intermediate
section 32 of the second branch passage 28 extends outside of the
end cover 17 between the first upper outlet section 30 and the
first core cooling section 31. Specifically, one end of the first
upper outlet section 30 is attached to an inner surface of the end
cover 17 around a through hole formed on the end cover 17, and one
end of the first intermediate section 32 is attached to an outer
surface of the end cover 17 around the through hole, so that the
first upper outlet section 30 and the first intermediate section 32
are joined to each other through the through hole. On the other
hand, one end of the first core cooling section 31 is joined to the
other end of the first intermediate section 32 in a liquid-tight
manner.
[0033] As illustrated in FIG. 4, the first core cooling section 31
is formed in the rotary shaft 2a of the first motor 2. In order to
supply the oil to the rotor 2b of the first motor 2 from inside, an
outlet hole 31a is formed in the first core cooling section 31 to
penetrate through the rotary shaft 2a in a thickness direction.
Thus, in the second branch passage 28, the first upper outlet
section 30 and the first core cooling section 31 are formed in
series. Therefore, a pressure loss in the second branch passage 28
is governed by an inner diameter and a length of the second branch
passage 28, a total opening area of the outlet hole(s) 30a and the
outlet hole 31a, and so on. That is, the pressure loss in the
second branch passage 28 may be adjusted by changing diameters and
number of the outlet hole 30a and the outlet hole 31a.
[0034] As illustrated in FIG. 2, the third branch passage 29 is
branched from the second oil passage 24 at a branching point 29a
that is downstream of the branching point 28a of the second branch
passage 28. The third branch passage 29 comprises: a second upper
outlet section 33 as a third oil feeding section that supplies the
oil to a coil 3c of the second motor 3 from above; a second core
cooling section 34 as a fourth oil feeding section that supplies
the oil to a core of the second motor 3 from inside; and a second
intermediate section 35 extending between the second upper outlet
section 33 and the second core cooling section 34.
[0035] The second upper outlet section 33 extends substantially
parallel to a center axis of the second motor 3. In order to supply
the oil to the coil 3c of the second motor 3 from above, the second
upper outlet section 33 is situated above the second motor 3 in the
motor case 16. FIG. 5 shows a structure of the second upper outlet
section 33 in more detail in an enlarged scale. As illustrated in
FIG. 5, a plurality of outlet holes 33a are formed in the second
upper outlet section 33 in such a manner as to penetrate through
the pipe forming the second upper outlet section 33 in a thickness
direction. The oil flowing through the second upper outlet section
33 drips from the outlet holes 33a to the coil 3c of the second
motor 3 thereby drawing the heat of the coil 3c of the second motor
3. Then, the oil further drips from the coil 3c of the second motor
3 to the oil pan, and pumped up again by the oil pump 6 to the oil
cooler 21 to be cooled again.
[0036] As illustrated in FIGS. 2 and 5, the second intermediate
section 35 of the third branch passage 29 extends outside of the
end cover 17 between the second upper outlet section 33 and the
second core cooling section 34. Specifically, one end of the second
upper outlet section 33 is attached to the inner surface of the end
cover 17 around another through hole formed on the end cover 17,
and one end of the second intermediate section 35 is attached to
the outer surface of the end cover 17 around another through hole,
so that the second upper outlet section 33 and the second
intermediate section 35 are joined to each other through another
through hole. On the other hand, one end of the second core cooling
section 34 is joined to the other end of the second intermediate
section 35 in a liquid-tight manner.
[0037] As illustrated in FIG. 5, the second core cooling section 34
is formed in the rotary shaft 3a of the second motor 3. In order to
supply the oil to a rotor 3b of the second motor 3 from inside, an
outlet hole 34a is formed in the second core cooling section 34 to
penetrate through the rotary shaft 3a in a thickness direction.
Thus, in the third branch passage 29, the second upper outlet
section 33 and the second core cooling section 34 are formed in
series. Therefore, a pressure loss in the third branch passage 29
is governed by an inner diameter and a length of the third branch
passage 29, a total opening area of the outlet hole(s) 33a and the
outlet hole 34a, and so on. That is, the pressure loss in the third
branch passage 29 may be adjusted by changing diameters and number
of the outlet hole 33a and the outlet hole 34a.
[0038] In the cooling system according to the embodiment of the
present disclosure, the oil discharged from the oil pump 6 is
delivered to the oil cooler 21 through the first oil passage 23. In
this situation, the oil flowing through the first oil passage 23 is
partially supplied to the power split mechanism 4. As described,
since the orifice 26 is arranged on the first branch passage 25, an
appropriate amount of the oil is supplied to the power split
mechanism 4. The oil supplied to the power split mechanism 4 drips
to the oil pan.
[0039] Heat of the oil delivered to the oil cooler 21 through the
first oil passage 23 is drawn by the cooling water. Then, the oil
thus cooled by the oil cooler 21 is delivered to the second oil
passage 24, and distributed to the first motor 2 through the second
branch passage 28 and to the second motor 3 through the third
branch passage 29. Thus, the oil circulating through the cyclic oil
passage 22 is partially delivered to the power split mechanism 4,
and the remaining oil is distributed to the first motor 2 and the
second motor 3. However, a flow control valve, an orifice or the
like is not arranged on the cyclic oil passage 22. For this reason,
an energy loss of the oil pump 6 derived from an increase in a
pressure loss in the cyclic oil passage 22 can be reduced with a
simple structure. In addition, since the second branch passage 28
and the third branch passage 29 are formed in parallel, the
pressure loss in the cyclic oil passage 22 will not be increased
compared to a case in which the second branch passage 28 and the
third branch passage 29 are formed in series. Whereas, the first
upper outlet section 30 and the first core cooling section 31 are
formed in series in the second branch passage 28, and the second
upper outlet section 33 and the second core cooling section 34
formed in series in the third branch passage 29. For this reason,
feeding amounts of the oil to the first motor 2 and the second
motor 3, and pressure losses in the second branch passage 28 and
the third branch passage 29 may be adjusted by changing diameters
and number of the outlet hole 30a and the outlet hole 33a.
According to the embodiment of the present disclosure, therefore,
the oil can be supplied to the power split mechanism 4, the first
motor 2, and the second motor 3 in appropriate amounts. Further,
since the oil cooled by the oil cooler 21 is delivered to the first
motor 2 and the second motor 3, the first motor 2 and the second
motor 3 may be cooled efficiently. Furthermore, since the second
branch passage 28 and the third branch passage 29 are individually
formed mainly of the pipe material, design flexibility of the
second branch passage 28 and the third branch passage 29 can be
increased.
[0040] Although the above exemplary embodiments of the present
disclosure have been described, it will be understood by those
skilled in the art that the present disclosure should not be
limited to the described exemplary embodiments, and various changes
and modifications can be made within the scope of the present
disclosure. For example, not only a mechanical pump but also an
electric oil pump may be adopted as the oil pump 6.
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